System for measurement and control



May 12, 1942- F. w. wHlTLCcK `2,282,442

' SYSTEM FOR MEASUREMENT AND CONTROI;

Filed 'April 7, 193s 5 sheets-sheet 1 Il f1 MWL .' (105th Opf" .18

May 12, F w` wHlTLocK 2,282,442

SYSTEM FOR MEASUREMENT AND CONTROL May 12 1942 F.'w. wHlTLQcK 2,282,442

v SYSTEM FOR MEASUREMENT AND CONTROL Filed April '7, 1938 3 Sheets-Sheet 5 j 9p 5 F7 @o 6.

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` It constitutes aniniproaement upon theaheatins control'l systemstdeseribedfand cleimedntthe-eotendina-application:eef: Edwin D. Witt Coleman, Serial VINO. 138,6;137led' Auglltaw; I110W:Patent 2:1:44el05f-Ianuarys-1'l .3 9,fandtin.myeeopendf ,ingr-application"Serial No l'atiiiflledtFebruary 9; daam'lhe. Coleman tem-employs atsystem of. yilvlieatsto.ne :bridge-@circuits fferf' rst measurins mom -temperatureandzaeontrollingtthe'frateof heat input-t9, the; roomfso .tot-tend toi-mein.- tamfthattempe ature :constant and for secondly subjecting thefrat Aof heatfmputto maximum-and minimum@ limits ;w,-hiehfare determined chiefly-by theloutdooratemperature. fylngtheoleman system thefmeasurement:ofi thefoutdoontemperaturei and the determination of the ratei-ofwheattherefrom arefaccomplished by; ar. singlemeasurement 0f a conditiony dependentfupongboth theeoutdoorvtemtperaturelandnthe f rate fat which gheatpis; vdelivered .1t ,fthetroomt For? examplealimitgbridgep circuit Ine sures/ta' weightedeaveragee of; outdoor stem;- .neratureiandfthe temperaturetoffsome art, ofthe "hQ/nggsytd fango/fu varend-:inf thesystemsfshown in myafaforementioned -copending applicatonscgthe:measurements'oftjroem temperaturee areiemodiiedrzbstw fot-hert measure- {mentsi for examples1 hegmeasurementofmthe froom enmera re meybermodied'baefmeasure- VIller-1t;oft:heating: systemfrtemperaturesor or the `operated .lpositipntoft at-valvegto Providern; rebel- `arruinar typecofgt ontrol s vment orf-room temper ''by .A 0.., tempera- .l 1e esireble levi-that the .relatrve welshtinso livrent/values l efteringgjnto a;palv lcular, eA i ux'lement'beeadjustableggso tirati the rvt@relative eiects may be regulated. ,Such adjustments fslope ladjustrnerlts since. sth ellative effectiveoiany LWO Itemperatures entering into a single measurementmay be/tdened -interms of theslopeyoftl the curveE representing the relation betweenthose twoatemperatures. The positions oft-such curves aregmostl Qnyeniently defined in terms o@ their interceptsi ithaxes having ypeculiarfsignicance in-the., itheorytor design of the systexngtor with axes relating to a condition of operation that is easily determined without the aid of measurements by the control system it- 1aya be termed it `MlmsUmtMErrr AN @CONTROL Freeport, Ill.,"'assignol to Micro "tion, Freeport; Ill., a corpora- Appu'euqaapm 7, 193s, serial-No. 200,810

(Cl.v 236-78) selfm Accordingly the adjustments and operationvfofthe system lare conveniently dened and described in terms ofthe slopes of these various pergt'xormance curves and their intercepts with the axismo'i normal room., temperature or condition of `zero heat input. Because these particular intercepts serve as thmost convenient reference for the adjustment, design and calibration of any particular system itnls desirable that these particular intercepts be'` adjustableentirely independently of each othnland of all other adjustments, and thatmo'j dj'ustment once made be disturbed by the ments. y. I mi ,:Frequently it isgdesir'able to control according toa number xof different .independent measurements .eacl'iloik which depends at least in part upon .the same., temperatur `Thus for example a sysen .annoying a prim Lif room entre and a secondary rate, of heat' "mit control may require that/,Leach ,of two limit measurements ,and the may' varyltrom time to time by values large "enough compared to the resistancechanges of the thermometer itself, that contact resistance introduced directly in circuit with the temperature `measuring' element seriously interferes with the measurement of the temperature values.

provision'of an improved circuit for taking measmoments-dependent upon a number of independiently measurable conditions, and the provision 40iof a system of temperature measuring electrical bridge circuits wherein a number of individual temperature measuring elements and the like may :be-combined in various ways for permitting a variety of individual control functions, wherein the relative; effectivenesses of such individual ele- `Aments. may lbe separately adjusted for each individual measurement and wherein the adjustments-forieach individual measurement are en.

' A out of their respective electric circuits, and the making of any other adfust- A Objects 'ot the present invention include the 1 "provisionrofa new and improved system of elec "tric measuring circuits of the bridge type, the

` respect to the operation of switches, that occasional irregularities in contact resistance values will not seriously disturb the operation of the system. Still other objects include the provision of a new and improved system for combining the effects of separate temperature responsive elements or the like in a single measurement, and the provision of an improved and simplified temperature. control system. These and other objects and advantages of the present invention will become apparent from the following description of certain speciflc embodiments of the invention, which embodiments serve by way of example to illustrate the manner in which the invention may be put into practice without thereby limiting the invention to the details of any particular illustration or example. In the drawings:

Fig. l is a partially schematic diagram of a temperature control system embodying my present invention; Fig. 2 is a somewhat simplified and conventionalized diagram of 'the electrical circuits of the system of Fig. l for the purpose of facilitating the explanation and description of the apparatus; Figs. 3 and 4 are graphs illustrating the operation of the system of Figs. l and 2:

Fig. 5 is a fragmentary diagram similar to the diagram of Fig. 2 illustrating a modification of the system of Figs. 1 and 2; and,

Fig. 6 is a circuit diagram similar to the diagram of Fig. 2 illustrating still another modification of the system of Figs. 1 and 2.

In accordance with one manner of carrying out my present invention I connect the measuring elements or resistance thermometers for each separate 4temperature measurement in a separate main bridge branch across the terminals of the power supply, connect a coupling branch containing resistors or a potentiometer, between center points of two separate main bridge branches, and make the galvanometer connection, not in the usual manner to a midpoint of a main bridge branch itself but rather to a point on the coupling resistor or potentiometer of the coupling branch. Movement of the galvanometer connection along this coupling branch serves to alter the relative effects of the two separate bridge branches upo n the potential of the galvanometer connection. Furthermore where two or more independent measurements 'are to be made involving the same bridge branch, separate coupling resistors or potentiometers are connected to the various bridge branches and switches are interposed in the coupling branches so that the circuits may be completed through only the particular coupling resistors involved in the particular measurement being made. I provide no switches lwhatsoever in the main bridge branches, but place all switches in the coupling branches, and give each coupling branch a total resistance that is high comparedto the probable variation of its switch resistance. Furthermore, I so locate the contacts in the coupling branch that their occasional failure to operate will simply prevent the system from exercising its usual control function rather than cause the system to control improperly, or alternatively, I so locate the switch contacts that their failure will leave the galvanometer connected to that one of the two main bridge branches which means generally is required to exert the greater effect upon the galvanometer.

In Fig. 1 a boiler III supplies steam under control of a motor operated valve I2 to the heating system of a building (not shown completely) which system includes a steam radiator i4. The operation of the valve I2 is controlled by a galvanometer or galvanometer relay i8 included in a system of temperature measuring Wheatstone bridge circuits now to be described. In all, three different bridge arrangements control the gal vanometer relay I8 at different times. These three different bridge arrangements are separate and distinct from each other but are composed of a number of common measuring elements. A group of cam operated switches driven by a motor Il operate to complete each bridge arrangement separately and to connect the galvanometer to it.

All of the various pairs of bridge arms or main bridge branches are connected across terminals 2li and 22 of a direct current power supply represented generally by the reference numeral 2l. One main bridge branch. or pair of bridge arms, includes a fixed resistor 28, a potentiometer 28 operated in unison with the motor operated valve I2, and a second fixed resistor 30. A second main branch includes fixed resistor 32, a centering potentiometer 8l, and a second fixed resistor 32. A coupling potentiometer 38 is connected between the center tap of the centering potentiometer ll and the center tap 29 of the valve 'potentiometer 28, and the center tap 31 of the coupling potentiometer 38 is connected to one terminal I5 of the galvanometer I6. The valve potentiometer 28 serves to rebalance the bridge circuit in response to each operation of the valve I2, and the magnitude of the rebalancing effect, is determined by the setting of the valve coupling potentiometer 86.

A third pair of bridge arms (shown at the top of the diagram) includes a temperature sensitive resistor or window thermometer 40, a group of three potentlometers l2, M and 48 connected l, 'in parallel with each other, and a fixed resistor 48. 'I'he window thermometer 4U is mounted in good thermal engagement with the inside surface of a window glass to provide an index* of outdoor temperature. f A fourth pair of .bridge arms includes a temperature sensitive resistor or room thermometer 58, a centering potentiometer 52, and a fixed resistor 54. The room thermometer 58 is located in the room at a position remote from the radiators, as for example on an inside wall, and so gives to the control system a measure or index of room air temperature. A fifth bridge branch includes a resistance thermometer 56 located above the radiator I4, a centering potentiometer 58, and aresistance thermometer il! located below the radiator Il. The two radiator thermometers 58 andil are placed in the air flowing across the radiator. Together they give to the bridge system a measure of the temperature rise of air across the radiator and therefore give it an index of the rate of heat input to the rooms.

Connected between the center tap 45 of potentiometer u and a center tap 5l of the centering potentiometer 58 isa coupling potentiometer 82 and switch contacts 64 operated by the cam 65, the switch contacts being next to center tap 51 of potentiometer 58. The center tap 68 of the coupling potentiometer 62 is connected by switch contacts 88 to the terminal I1 of the galvanometer I6. When the switch conmets-.g l and nmrefrcloseefbyzcam- 56; inertivanonietcr` tests `I to f-'determine whether. :ore-not;

the heat 5 input l tobi-the room lisf above or vbelowv explained presently. Similarly there-isfconnected between the center tap41 ofthe potentiometer 46 and .the center; tap. .511- of potentiometer 58, switch contacts 'I0 and a coupling potentiometer 68 with the switch contacts 1 0"next to\the potentiometer 44.1l The center taploffpotentiometery 08 `is4 connectedrthrough switch -contact 'I2 vto lthe galvanometer I8. vr.When the yswitches 10 andf12 areclosed bylcamfll` thegalvanometer I6 test`to determine whetherv or notwthe-.rate of heat inputiis above or-below ythe -valuel setas the lowlimit of heat input. -v x The potentiometers 42 andV 1 52 'mayf be connected mechanically sothatethey are 'constrained to operate together. Theircenter tapsr43fand 53 have connected betweenthem a coupling potentiometer'flkand switchcontacts 16... with switch 16 next. to .the potentiometer -A2. The center .tap .15 of potentiometer 14t is..c onnected through, switch contact .1 8 the galvanometer I6 and when theioontactsf 'Iand 18\ a re closed by cam 11 Athe 'galvanometery respondstofa measurementrofroom temperature by .the ther.-

.mometer 50.vv yThis'measurementof'roometem-y peraturey is made4 to depend'` Vin lpart, uponthe 'windowthermometer 40 .so that: .the .rebalancing function of the valve potentiometer-20 neednot cause the control point of the room :temperature `todrop as the rate of heating-increases..in responsetoa drop of outdoor temperature. f

The galvan'ometerrelay- `|6 .;is;s ho wn :diagram- "matically as havingf a pair of.-; -contacts.-,6 and; `I 'adapted' to. A be closed/by the galyanometer. when itiv responds to. 4 funbalancedf con l tions .fofVj the bridge circuits. .These contacts- G and 1 lare `con- :nected ito.-v a pOwer.. supply 2 3 `and a reversible motor 25 through contacts 8,. 9 and I ,I-, operated by `cams 13,11 9 fand -.2I whichfinfturn aredriven byy thesame motor I 8. that Qperatesjcams 5,l 1|

fdiagrammatically.end the. means by; whiehwit controls-the .m otor .25. of the valye. 2 may-beof :ra typeshown in theColeman -Patent. No 2,144.1 g already referredrftp; 0r in my copending app at'ion serial No. fmolinled yAprilei938..l l. `.f-.--'11.1e motor I8 turnsin erleekwis directio o drivegthe cams ataslow rate, ,as .forg exampleat -vefspeedt 0f 011e `revolution rer minutein a l.cleek- .wise direction as vewed .in Fis. 1. Ae-.the meter i8 rotates. inf a eleekwise direction, the. camel",

tiene. 1lv ser operate. theirirspeetive eentaets .thatthe galvanometer in' tumlmsill'es the, .room

Each time that the galvanometer is connected forpnepf these, tests thecamgl closes the cont0 the-rQweremNy .23- iCamS '9.- endf..?lf"n.diher ewitehesltend. H serve to prevents sterline Qperetienef. the. valve inreepensetet1! Owilimit .test-.endl to` prevent aclosing operati mme-spense te a. high linut-te i l h p tentiometers 42,.44, 4'6a nd ,filare pro- .yided.wi th. graduatedfscales 80.182,.;84. and 86 whose mounting positions may be adjusted to calibrate them. The graduations of these scales The coupling potentiometers 62, v 69,"| 5 f6 aretalsoygraduated ibutare not e'iui'pp'y v adjustablescales. f y,

.Theffollowing. descrip fn of thedlutment and l operationlofthe system may best be. under;- stoodibylreierence-.tdFig. 2 which showsthe bridge@ circuitsf` of Fig.. f.1 in a somewhat Q simpler form a1tho the. Afiesenp tionjimplies alselgte Fig. 1.

Corresponding. parts yare indicated. by L,the same reference .numerals inthe .two gure's'. f.,

.Afterl installation the system is. initiallyad- .iusted.a s follows: Firstthe steam val v e l2 is moyed-.to its completely closed position'to b ring the valve potentiometer 28 to that setting which corresponds to zero heat'input; to theroom or space lt'i?1 be heated. The two radiator ther mometers 56 and 60 are: brought tolftlie same temperature, as for example by layingfthem next to eachsother. Preferablythey shouldbe at a temperature-near 70 F. but the exact' temperature isunimportant. The room thermometer and the window thermometer 40 should also be at temperatures near F. but their exact temperatures should belmeasured, as for example by means .of liquid thermometers. Motorfl is permitted to operate until it has rotated 4the cams i?I from the position in which they are shown v Fig.2 (extreme clockwise position as seen in Fig.\ l)' so that the potential of center tap 31 arid. otterminal I5 of galvanomter I6 is deter mined principally by the setting of valve poten tiometer 28 and only slightly by the setting of potentiometerl 34. Similarly center tap 63 of potentiometer 62 is moved to its lowermost position seen in Fig. 2 (extreme clockwise position as seenfin Fig. 1) so that the potential of center tap 03 and of terminal I1 of galvanometer I6 y is determined principally by the setting of potentiometer 58 and only slightly by the setting of potentiometer 44.

Potentiometer 58 is adjusted to bring the reading of galvanometer I6 to zero. Then the center tap 63 of coupling potentiometer 62 is moved towits' uppermost position as seen in Fig. 2 (extreme apunten-clockwise position as seen in Fig. 1 that its potential Jis determined principally isetting of potentiometer 44, and poten- `e r` 4 4 is adjustegdj to bring the reading of galvanometer I6 to zero These two adjustments .of potentiometrs 58 and -44 are only preliminary 2l, but il center tap I1 of coupling potentiometer Siisagainmovedtoltslowermostpositionas viewed in Fig. 2 the galvanometer li may deflect out of its nero'poaition. Individual adjustments of potentiometers Il, Il and Il should be repeated in turninthe mannerjust described until the coupling potentiometers It and 02 may be manipulated throughout the entire ranges of their adjustments without causing galvanometer i6 to deilect out of its zero position. When this adjustment is completed the center taps of potentiometexs Il, l, 3l and 28 all are at the same potential, and at the potential corresponding to zero rate of heat input to the space to be heated. Next the graduated scale l2 of potentiometer ll is adjusted to that position in which the center tap I5 indicates the exact temperature of window thermometer Il on the graduations of the scale.

Next the motor Il is operated until the cam 1l closes the switches 1l and 12. Then the potentiometer 46 is adiusted to bring the reading ol the galvanometer Ii to zero. inasmuch as potentiometers 5I and 34 already have been brought to their correct adjustments no further adjustments of those potentiometers are required in connection with the setting of potentiometer Ii. The adjustable scale I8 of potentiometer I6 is set so that center tap 41 indicates the exact temperature of window thermometer Il.

Next the motor I8 is operated until cam 11 closes switches 1i and 1l to complete the connections to the room coupling potentiometer 1l. Then the two potentiometers 42 and 52 are adjusted until the galvanometer I6 reads zero and so that the setting of the coupling potentiometer 1l may be changed without altering the aero reading of the galvanometer. Repeated adjustments of the two potentiomcters 42 and 52 may berequired. Then the calibrated scale Il of potentiometer l2 is set so that the center tap 43 indicates on the graduated scale Il the exact temperature of window thermometer Il and the graduated scale li of the potentiometer 52 is adjustedsothatthecentertap indicates on the scale Ii the exact temperature o! room thermometer 5I. If. potentiometer-s l2 and 52 are connected mechanically to be operated together, only one graduated scale will be required for the two of them.

The foregoing procedure complete: the adjustments of the system. There remain only the adjustmenm of the four coupling potentiometers 3i, i2, il and 1l. The potentiometers l2, Il, 46 and 52 having the-graduated and calibratedscalesareadaptedtoheadjustedfmm time to time to alter the temperatures to which the system controls.

A Room temperature control As is explained in my copending application, Serial No. 189,545 already referred to, one incidental eilect of the xebalancing fimction of the valve potentiometer 28 is to lower the temperatineatwhichthesystemtendstomaintainthe room air as the rate of heat input increases. Obviously the rate of heat input increases with valve opening. As the valve opens the tap 2! movestotheieftasseeninrigandsomakes the tap 2l more positive in potential. A part of this increased potential is imposed upon the lower terminal I5 of the galvanometer, the speciiic proportion being determined by the setting of the tap 31 of the coupling potentiometer 3i. Accordingly with the valve partially open, the bridge tends to balance (galvanometer It reads zero) for a somewhat lower room temperature as measured by the resistance thermometer Il, because the falling room temperature moves the potential oi' the tap l1 toward the positive. However, since the upper terminal I1 of the galvanometer is not connected directly to the tap 53 but rather to the center tap 15 of the coupling potentiometer 1l, the particular room temperature requiredto bring the bridge to balance depends partly upon the temperature of the window thermometer Il, and the window thermometer will have its maximum eiect when the tap 15 is moved to its extreme upper position as seen in Fig. 2 (extreme clockwise position is seen in Fig. 1).

The best setting of the tap 2l of the potentiometer Il is that setting at which tap 21 is moved down as seen in Fig. 2 only far enough to just prevent objectionable fluctuations of room temperature, when the system is controlled accoi-ding to room temperature alone. With the potentiometer 36 at its best setting as just dened, potentiometer 1I should be so set that the control point remains substantially constant for all weather conditions, that is so that the system tends to maintain the room at the same temperature for all weather conditions.

'I'he adjustment of center tap 31 of potentiometer 36 can best be made when the outdoor temperature is well below the room control point, as for example, when the outdoor temperature is low enough to require'at least 30 percent of the maximum opening of the steam valve l2. During this test the position occupied by center tap 15 of coupling potentiometer ll is not particularly important, but preferably should be moved to its lowermost position as seen in Fig. 2 (extreme clockwise position as seen in Fig. 1) so that the outdoor temperature as measured by window thermometer Il will have substantially on eifect on the operation of the system. The system is put into operation with the adjustable tap 31 of coupling potentiometer 3i set to its uppermost position as seen in Fig. 2 (extreme counterclockwise position as seen in Fig. l) so that the valve potentiometer 28 will have little or no effect on the control of the valve operation. While the system as so set, will tend to maintain constant temperature of the room air, the control will hunt and the room temperature will fluctuate badly. While the system is operating, the adjustable tap 31 is gradually moved down as seen in Fig. 2, so as to increase gradually the rebalancing eli'ect of the valve potentiometer 28 upon the bridge circuit. This adjustment of coupling potentiometer 36 is made in small steps over a considerable period of time, and its tap 31 is moved down as seen in Fig. 2 only far enough to reduce the iiuctuation of the room temperature to an unobiectionable value while the outdoor temperature, and therefore the heating load, remains substantially constant. [hiring this adjustment of the potentiometer 31, the system need not necessarily have controlled the room temperature at the most comfortable value.

The correct adjustment of the potentiometer 1l depends in part on the question of comfort in the space to be heated. Accordingly the potentiometer 52, which selects the room temperature control point, is set to that position of its calibrated scale Ii which indicates the desired room temperature for mild weather conditions (requiring light heating load). Then the system is put into operation under a substantial vanometer.

heating load with the potentiometer tap 15, at the beginning of the test, still in its lowermost position fa's'seenin Fig. 2. While the system is operatinggthertapul is moved far enough up as seen' infFig; :21 (turned far enough counterclockwisefas seen in Fig.; 1) to make the system hold the roomatthe-.desred temperature. 'I'his temperature ati which: the system holds the room under conditions ofi substantial heating load need notfbethesame as that indicated by the setting of fthef control-point-selecting-potentiometer 53 onf'its calibrated scale 86, but may be higher or lower than that value. The scale 86 indicates only the nominal control point. The influences-of the window thermometer 40 and with the 70 degree mark at the origin to corre-tif spond to a room control point of 70 degrees.

the rebalancing potentiometer 36 permit the actual control pointto deviate from that nominal value except under mild weather conditions when the heating load is slight.

The separate effects of the settings of poten-VY tiometers 3E and 14 may be best illustrated by the graph of Fig. 3. In Fig. 3, the control point or temperature at which the system tends to maintain the room is plotted as ordinates against the rate of heat input as abscissa. As previously explained one effect of the rebalancing type of control is the lowering of the control point as the rate of heat input increases. This condition is represented by the drooping curve 92. The angle at which this line 92 dips down is determined by the setting of valve coupling potentiometer 3B, and the dip of the curve increases as the center tap 31 of potentiometer 3S is moved down as seen in Fig. 2 to increase the effect of the valve potentiometer 28 on the gal- The point 90 in Fig. 3 at which the curve 92l intersects the axis of zero heat input is determined substantially by the adjustment of potentiometer 52. In general, the two potentiometers 52 and 42 should be set to indicate the same temperature on their graduated scales. While outdoor temperature is not plotted as such on the vcurve of Fig. 3, the outdoor temperature, generally determines the required rate of heat input which appears as the independent variable in the graph of Fig. 3, and therefore insofar as the quantitative relations indicated in Fig. 3 are concerned, it may be assumed for the time being that outdoor temperature and rate of heat input vary together. InasmuchA as the potential of terminal I1 of galvanometer- I6 is determined not only by the setting of potentiometer 52 but also by the setting of potentiometer 42, that poential in turn is determined in part by the outdoor temperature. The effect of outdoor temperature on thev galvanometer raisesthe curve 92 in Fig. 3 to a position such as 94 as shown in dotted line, in which position the curve still intersects the axis of zero heat input at the point 90. The angle through which this control point curve is raised by the outdoor temperature as measured by the window thermometer 40 is determined by the setting of coupling potentiom- .eter 14, the effect of outdoor temperature being greatest when center tap is moved to its uppermost position as seen in Fig-,2.

Limit controly i In Fig. 4, the rate of heat` input is plotted as ordinates against the diierence between the room control point and outdoorftemperature as abscissa. 4The point of originA oi theI axes is taken at zero heat input and zero ltemperature difference. The axis of abscissas is', marked off in values ofv temperature of the window thermomi accordingly theffcurf The curve 96 represents" apprpxmateI-y?meure; iiipiit to efpajrucuiar quired variation in lhe iiiiiiiiiii wiiii ciiiiiiiii iiiiiiiiiiiipiiiiiiiiiiiiiiii iii' a control point-g` d V controlled to remain atil'lfuthe to zero and the, wind when-the outdoor' te atur reaches4 70, and;

ture of 70. This in roept"38"is7deterinined by the same adjustme determines the inter# cept of Fig. 3, AWely-,tirezadj,istrrierit ofthe two potentiometersv '42 fand 52." "I 'lf1e"s`1ope "or the curve as, that isjihiiv rate et which, ure-heat de: mand increases withja Vfall of 'outdoor tempera@ ture, depends principally upon 1the characterisl tics of the building beingfcontrolled'but depends f also to some extent upon the droop'orjri'sefof"` the'curve 92 in Fig. 3, since forjexample'i the room control point falls with a dropiri out -door temperature the fall of the control point represents a reduction in the diierenceibtween insid'e and outside temperature and Vconsequently causes the curve 96 in Fig. 4 to rise less'ste'eply.

It is desirable that the rate of heat input be subjected to maximum and minimum limits'fas represented by the two limit curves |00 and |02 in Fig. 4. Obviously the upper limit curve v|00 should lie wholly above the nominal requirement curve 8B and the lower limit curve |02 should lie wholly below the curve 96. The diierence between the maximum and minimum limits permits the room to regulate the rate of heat input within those limits, and so to accommodate such variations in heat demand as may be caused by changes in the wind or solar conditions or the opening of windowsor the like. The point of intercept |04 of the upper limit curve |00 with the outdoor temperature axis 81 corresponds to the setting of the calibrated potentiometer 82 of` Figs. 1 and 2. Similarly the intercept |06 of the lower limit curve |02 corresponds to the setting of the calibrated potentiometer 46 of Figs. 1 and 2. The slopes of the two limit curvesv|00 and |02 are determined by the setting of the coupling potentiometers 62 and 68 respectively. The system initially should be put into operation with the center tap 63 of coupling potentiometer 62 set to its uppermost position as seen in Fig. 2 (its extreme counter-clockwise position as seen in Fig. 1), and with the center tap 69 of coupling potentiometer 0 8 set to its lowermost position asV seen in Fig. 2 (extreme clockwise position as seen in Fig. 1). These settings will give the upper limit curve |00 its maximum slope to makeit take a position such as |08, and give the lower limit curve |02 its minimum slope to mak'iit take a position such as I0. The system when so adjusted and put into operation will controlsolely in accordance with room temperature vas measured by the room thermometer 50v"and asico'rrectedv by ,the window thermometerr 40 for* preventing the suppression of the-control pin't.

' Then with the outdoor temperature holdingflsiib.-

nput goes' goes i703 as, iriiriiifiiS- the xii fori? abscissas at theffpoin 98" at the window temperalextent or amount of this rebalancing action, has already been brought to its proper adjustment. The control system will then have brought the rate of heat input to the proper value for the outdoor temperature then prevailing and presumably the values of window temperature and rate of heat inputv will correspond to some point on the nominal requirement curve 96 in Fig. 4. The motor I9 is stopped in the position in which cam 65 holds the switches 64 and 66 closed to connect the upper limit bridge system to the galvanometer I6. The calibrated potentiometer 44 is set to the same temperature reading as the potentiometer 42, to bring the intercept |04 in the diagram of Fig. 4 in to coincidence with the intercept 98. Then the potentiometer 62 i's adjusted to bring the galvanometer to zero to rotate the curve |08 about the coinciding intercepts 98 and |04 and make it coincide with the curve 9S. In this position the upper limit curve |00 has a known orientation and location with respect to the curve 96 and so may easily be moved therefrom to its correct position. Next the potentiometer 44 is adjusted to a temperaturesetting above that of the potentiometer 42, as for example above, to separate the intercept |04 from the intercept 96 as shown in Fig. 4 and the center tap 63 of potentiometer 62 is moved slightly upwards as seen in Fig. 2 (counter-clockwise as seen in Fig. l) to make the curve |00 diverge slightly from the curve 96.

Similarly the motor i8 is next stopped in the position in which cam 1I closes switches 10 and 12, the potentiometer 46 set to correspond to the setting of potentiometer 42 and the potentiometer 68 adjusted to bring the galvanometer to zero to' make the lower limit curve |02 coincide with the curve 96. Then the potentiometer 46 is set to a value a few degrees below' the setting of the potentiometer 42, and the arm 69 of the potenti.- ometer 68 moved down slightly as seen in Fig. 2 to make the curve |02 lie below the curve 96 and to diverge therefrom.

A coupling potentiometer, such as the potentiometer 62, bridged between the two center points of a pair of bridge branches, such as the window .thermometer branch and the radiator thermometer branch provides an extremely reliable and wide range of adjustment of the relative effects of those two bridge branches upon the galvanometer. For example, an adjustment of the slope of the curve |00 by means of the coupling potentiometer 62 can have no effect whatsoever upon the position of the intercept |04 of that same curve, because the position of the intercept is determined entirely by the setting of the potentiometer 44. The range of adjustment of the slope is determined entirely by the relative values of the total resistance of coupling potentiometer 62 and the resistances of the two bridge branches between which it is connected. A high value of resistance for the potentiometer 62 provides the greatest range of adjustment of the slope of the curve.

The arrangement of switches 64, and 16 whereby only one of the coupling potentiometers 62, 60 and 14 is connected between the center points of its respective bridge branches at a time prevents the adjustment of the slope or intercept of any one curve from having any eiect whatsoever upon the slope or intercept of any 'other curve. Furthermore any number of control functions may be performed with only one set of thermometers or other control devices, such as for example the valve potentiometer 28 or window thermometer 40 (which may be required to be locatedlremotely from the main portion of the apparatus). Furthermore the present arrangement, while permitting all functions and measurements to be accomplished with one set.of thermometer elements, does not require that the bridge branches containing those thermometers etc. be opened and closed by switch contacts. Obviously switch resistance introduced in series with the galvanometer I6 itself, as at the contact 18, can not disturb the bridge balance but can only slightly reduce the sensitivity of the galvanometer I6 to any unbalanced condition of the bridge circuit. While resistance introduced in series with the coupling potentiometer itself, as for example at the contacts 64 will disturb to some extent the balanced condition of the bridge circuit, the several contacts 64, 10 and 16 are so arranged in the circuit with respect to the functions which they control that the operation of the system will not be disturbed materially by high resistances appearing occasionally between those contacts as a result of dirt or the like between the contacting surfaces. Thus, for example if the contacts 64 should fail entirely to close, the upper limit curve |00 (in Fig. 4) would move away from the nominal curve 96 and assume a vertical position through the intercept |04, and consequently would simply fail to impose the high limit of heat input upon the operation 'of the system. An occasional failure of this type can cause no serious mis-operation of the system. Similarly if the contacts 10 should fail to close, they would simply leave the potential of the center arm 69 of the coupling potentiometer 68 unaffected by the window thermometer and accordingly would rotate the lower limit curve |02 about the intercept |06 away from the nominal curve 96 into a horizontal position where it would coincide with the axis of ordinates. Accordingly an occasional failure of the switch contacts 10 lsimply causes the system to fail to impose the lower limit of heat input and consequently can not induce any serious misoperation of the apparatus. A failure ofthe contacts 16 to close would leave the room temperature unaiected by the window thermometer and would cause the system temporarily to tend to control the room temperature in accordance with the curve 92 of Fig. 3 wherein the control point is depressed by the operation of the rebalancing valve potentiometer 28. But an occasional and temporary disturbance of this kind could not seriously interfere with the control operations of the, system. Ordinarily there are only a few degrees difference between the correct control point on curve 94 of Fig. 3 and the corresponding point of curve 92. Those few degrees represent the maximum error, and that error could occur only when the switch contacts would fail to close at all. A "dirty or high resistance engagement of the switch contacts would introducean error less than that maximum. Furthermore the inherent time lag of the room control would not permit such a small error to introduce any appreciable mis-control unless the contact trouble should persist through succesive switch operations over a long period of time. Any detrimental effects of variable contact resistance of switches 64, 16 and 10 in the coupling branches are minimized by making the resistance of each coupling branch high compared to the probable range of variation of the switch contact resistance, and .high compared to the resistance change that the main bridge arms (of which there are two in cach main bridge branch) experience during the operation of the system. l 1 i s Fig.f5illustrates ai modification of a portlonjof thesystem of Figs. 1v and;2 wherein the coupling potentiometer is replaced'byl twov resistors I I0 and II2 connectedinlseries, of which-resistor I2.is

variable; Tlieconnection tothe galvanometerly through thefs'witch 66 isgtakeny oi at theipoint between tliesetwo resistors -IIIIand H2. .Inas.` much as the slope `of thefupper-.limit curve IIJII foff.y

Fig. 4 ordinarily willt not be vcarried belowrthe.

curve 96, the full" rangeofadjustment provided by the potentiometer 63 of Figs. 1 and-.2 isnotw required and accordingly the range of adjustment y range of adjustment as does the arrangement of Figs. l and 2, it does provide a more sensitive adjustment in the range that it does cover.

In the modication of Fig. 6 the several adjustments provided by the potentiometers 42, 44 and 46 in'Fig.-1 are eliminated. The window thermometer 40 is connected in series with three resistors II4, II6 and 48. The resistors I I4 and I I6 have just suicient resistance to separate the connections to the several coupling potentiometers 62, 14 and 68 by intervals corresponding to intervals of 10 degrees Fahrenheit of outdoor temperature as measured by the window thermometer 40. Accordingly the temperature intervals between the limit curves are determined by the resistors II4 and II6 and are not adjustable. In addition the centering and adjusting potentioxneters 52 and 58 are eliminated and instead mometers 40 and 50. Potentiometer 34 is set tot indicate the-desired vroom temperature and the apparatus ls put into operation with -the center jy; tap'63fof potentiometer, 62 and center tap 31 of potentiometer 36in` their Iuppermost positions and' with .the cente'rtaps 15and 69 of the potentiomei tersv Hand 18 in their lowerinost positions so that vthe -heat .input will be controlled primarily in accordance with room temperature. The" center .tap V 31 of potentiometer 36 should be moved upwardjust far enough to overcome objection;y able v.fluctuations of room temperature. Next the Y tap15 ofnpotentiometer14 is adjusted upward. l justenough toy provide a sufliciently highfcontrol ,1

point with the .outdoor temperature considerably belowthefcontrolpoint of the room.` Next fthe switch operating mechanismisstopped with the switch=66 closed and switches 12 and`18 open.l

. The center tap 63 of potentiometer 62 is moved the centering potentiometer 34 is provided with a graduatedscale I I8 which is adjustable for purposes of Calibrating the system. Consequently the bridge system of Fig. '6 makes no provision for initially bringing all bridge branches to perfect balance under conditions of zero heat input.

In addition the system of Fig. 6 elminates the switches 64, 1D and 16 in series with coupling potentiometers 62, 14 and 68. The only initial or calibrating adjustment provided in the wholel system is the adjustment of the position of the graduated scale I I8 for the potentiometer 34. In the system ofFig. 6 the potentiometer 34 serves as the adjustment for selecting the control point at which the system tends to maintain the room temperature.

The initialv adjustment of the system o f Fig. 6 is made, as follows: Switch 12 is closed and switches 66 and 18 are opened to connect the effect upon the galvanometer I6, the potentiomefter 34 is adjusted to bring the galvanometer deection to zero, that is to balance thesystem. Graduated scale II8-is adjusted so that center tap of potentiometer 34 indicates the measured temperature of the room and window therdown until the galvanometer comes to zero and then` is moved slightly upward to space the upper limit of heat input somewhat above the average.,heat requirement. Next `the switch 18 is closed and `with the switches 66 and 12 open the center tap 69 ofthe potentiometer 68 is moved up till the galvanometer comes to its zero or rest position,y and then the center tap 69 is moved down slightly to space the lower limit of heat input slightly below the average heat requirement..V

`The selection of the control point or temperature at which the system tends to maintain the rooms of the building ismade by adjusting the potentiometer 34 in accordance with its gradu- -ated and calibrated scale I I8.

The system of Fig. 6 is simpler in construction and initial adjustment than that of Figs. 1 and 2 because it eliminates many of the adjustable elements of the system of Figs. 1 and 2. In many cases the simplied system is to be preferred because the absence of manually adjustable elements prevents persons unacquainted with the purposes of the several adjustments from inadvertently disturbing the settings. However, it is desirable in certain instances to provide the extreme flexibility that the numerous adjustments give the system of Figs. 1 and 2.

It .will be apparent that the specific `embodiments of the present invention herein illustrated andvdescribed are offered merely as illustrations and examples, and that the invention is capable of numerous modifications and variations.l For` example, the system may be applied to other typesof heat interchange systems, such as refrigeratingsystems, and also may be applied to the measurement and control of conditions other than temperature. The invention is notlimited in all respects to bridge circuits Aofthe direct type or of ltheresistance type, nor to the use of DArsonvalcgalvanometers, andwherever the` term galvanometer appears inthe claims it shallbe conl strued to include all types of instrumentsv respon2 sivetothe iiowvof electric4 current orto. the presence otelectricvpotential. Neither is thelinvention limited-K to resistors' and the .like thatl change their inherentimpedance with temperaturabu't it may. employ mechanically adjustableimpedance., devices `operated by thermally responsive actuators and the like. y ",'LQ

Accordingly the invention is to be limited only 'inaccordance with the scope `of thevlappen'ded `claims...`vv y Y'. l;

l systemfan.electric measuring bridge circuit'comf prisingftwolmain ybridge branches connectedin wir parallel. each of said two main bridge branches including condition responsive current controlling element therein, each said main bridge branch having an output point intermediate its ends, an impedance coupling branch connected between said outputI points of said main bridge branches. said coupling branch having an adjustable potentiometer. the adjustable tap of which constitutes an adjustable output point for said coupling branch intermediate the points of connection of said coupling branch to the output points of said two main bridge branches, and an output connection to said output point of said coupling branch, whereby said potentiometer may be adjusted for varying the relative values of impedance between the output point of said coupling branch and the respective output points of said main bridge branches.

2. In combination in an electrical measuring system, a bridge circuit comprising three main bridge branches connected substantially in parallel, a condition responsive current controlling element in one of said main bridge branches, said main bridge branches having output points intermediate the ends thereof, two impedance coupling branches each connected to output points of two main bridge branches, said one main bridge branch having both said coupling branches connected to it, each coupling branch having a separate output point intermediate the points or its connection to the output points of its two main bridge branches, and output connections to the output points of said coupling branches.

3. In combination in an electrical measuring and control system, an electrical measuring bridge circuit including two main bridge branches connected in parallel, a current controlling element in one of said main bridge branches responsive to a rst condition, a current controlling element in the second main bridge branch responsive to a second condition, an impedance coupling branch connected to said main bridge branches at points thereof intermediate the ends thereof, an output connection to said coupling branch at an output point intermediate the points of connection of said coupling branch to said two main bridge branches. a galvanometer in said output connection, regulating means responsive to said galvanometer for regulating at least one of said two conditions to vary a relation between said two conditions, but operable to vary said relation in only one direction of change, contacts for opening the circuit through said coupling branch, said contacts being so located in said coupling branch with respect to the point of connection of said galvanometer to said coupling branch and the points of connection of said coupling branch to said two main bridge branches that '1f said contacts should fail to close and an error should result therefrom in the response of said galvanometer to said two current controlling elements in said main bridge branches, such error would be in such a direction as to indicate to said galvanometer an error in the'value of said relation between said two conditions which error in said relation would be in that direction in which the gialvanometer could not tend to counteract the error.

4. In combination in an electrical measuring and control system, a system of electric bridge circuits including two main bridge branches in parallel, first and second current controlling elements connected in said main bridge branches respectively and responsive to a rst and second condition respectively, an impedance coupling branch between said two main bridge branches, an output connection to said coupling branch at an output, point thereof so located that there are unequalV impedances between the output point of said coupling branch and the points of connection of said coupling branch to said two main bridge branches, whereby the potential o! the output point of said coupling branch is more responsive to changes of said rst condition than to changes of said second condition, and electric switch contacts in said coupling branch for opening the circuit therethrough, said switch contacts being located only between the output point of said coupling branch and the point of connection of said coupling branch to said second main bridge branch.

5. In combination in an electrical measuring and control system, a system of electric bridge circuits including two main bridge branches connected substantially in parallel, a condition responsive current controlling element in one of said main bridge branches, an impedance coupling branch connected between said two main bridge branches, a terminal connection to said coupling branch at a terminal point thereof so located that there are unequal irnpedances in the two portions between the terminal point o said coupling branch and the points of connection of said coupling branch to said two main bridge branches, and electric switch contacts in said coupling branch for opening the circuit therethrough, said switch contacts being located in said coupling branch only to that side of said terminal point thereof on which lies the greater impedance of said coupling branch.

6. In combination in an electrical measuring control system, an electrical measuring bridge circuit including two main bridge branches connected substantially in parallel whose points of connection to each other constitute terminal points, a current controlling element in one of said main bridge branches electrically responsive to a controlled condition, an impedance coupling branch connected to said main bridge branches at points intermediate the ends thereof, terminal connections to said coupling branch at a terminal point thereof intermediate the points of connection of said coupling branch to said two main bridge branches, a galvanometer connected in the bridge circuit and having a connection to at least one of said terminal points and responsive thereby to said current controlling element, regulating means responsive to said galvanometer for regulating said controlled condition to vary its elect upon said current controlling element but operable to respond to said galvanometer to vary said condition in one direction of change more rapidly than in the other direction of change, contacts for opening the circuit through said coupling, said contacts being so located in said coupling branch with respect to the point of connection of said terminal connections thereto and with respect to the sense of response of said galvanometer to the changes in said controlled condition that should said contacts tail to close and an error result therefrom in the response of said galvanometer to, said controlled condition, such error would be in such direction as to indicate to said galvanometer an error in said value in the direction thereof to which the regulating means responds the less rapidly to alter said controlled condition.

7. In combination in an electrical measuring system, an electrical measuring bridge circuit comprising two main bridge branches connected substantially in parallel, one of said two main bridge branches including a condition responsive current controlling `element therein, each of said main bridge branches having a coupling point intermediate its ends, an impedance coupling branch connected between said coupling points of said main bridge branches, said coupling branch having a terminal point intermediate the point of connection of said coupling branch to the coupling points of said main branches, circuit connections to said terminal point of said coupling branch, and a switch in said coupling branch, the impedance of said coupling branch being high compared to the probable variation of the impedance value of said switch in its circuit closing condition.

8. The combination of claim 3, wherein said switch is located in one of the portions of said coupling branch between its terminal point and its points of connection to the two main bridge branches, and wherein the impedance of said portion of said coupling branch in which said switch is located is high compared to the probable variation of the impedance value of said switch in its circuit closing condition.

9. In combination in an electrical measuring system, a bridge circuit comprising at least two main bridge branches connected substantially in parallel, a condition responsive current controlling element in one of said main bridge branches, said main bridge branches having coupling points intermediate the ends thereof, two impedance coupling branches, each connected between a coupling point of said one main bridge branch and a coupling point of another main bridge branch, each coupling branch having a terminal point intermediate the points of its connection to its two main bridge branches, circuit connections to the terminal points of said coupling branches, means in one of said coupling branches operable for varying the relative values of impedance of its two portions between its terminal point and its two points of connection to its two main bridge branches, and a switch in said one coupling branch for opening the circuit therethrough between the two main bridge branches to which it is connected.

10. In combination in an electrical measuring system, a bridge circuit comprising at least two main bridge branches connected substantially in parallel, a condition responsive current controlling element in one of said main bridge branches, said main bridge branches having coupling points intermediate the ends thereof, two impedance coupling branches, each connected between a coupling point of said one main bridge branch and a coupling point of another main bridge branch, each coupling branch having a terminal point intermediate the points of its connection to its two main bridge branches, circuit connections to the terminal points of said coupling branches, one of said coupling branches having a total impedance which is not large compared to the impedance value of the rest of the circuits as measured between the two end points of said one coupling branch and a switch in said one coupling branch for opening the circuit therethrough between the two main bridge branches to which lt is connected.

11. In combination in an electrical measuring system, a bridge circuit comprising at least two main 'bridge branches connected substantially in parallel, a condition responsive current controlling element in one of said main bridge branches, said main bridge branches having coupling points intermediate the ends thereof, two impedance coupling branches, each connected between a coupling point of said one main bridge branch and a coupling point of another main bridge branch, each coupling branch having a lterminal point intermediate the points of its connection to its two main bridge branches, circuit connections to the terminal points of said coupling branches, one of said coupling branches including adiustableimpedance means operable for changing the total impedance value of said one coupling branch, said one coupling branch including also a switch for opening the circuit therethrough between the two main bridge branches to which it is connected.

12. The combination of claim 2 wherein one oi said output connections includes a switch for opening the circuit.to the output point of the coupling branch to which it is connected.

13. In combination in an electrical measuring system, a bridge circuit comprising two main bridge branches connected substantially in parallel, a condition responsive current controlling element in one of said main bridge branches, said main bridge branches having coupling points intermediate the ends thereof, two impedance coupling branches each connected between coupling points of said two bridge branches, each coupling branch having a separate terminal point intermediate the points of its connection to the coupling points of said two main branches, and terminal connections to the terminal points of said coupling branches.

14. The combination of claim 13 wherein one of said two coupling branches has an impedance value which is large compared to the impedance ofthe rest of the bridge circuit as measured between the coupling points to which said one coupling branch is connected.

FRED W. WHITLOCK. 

